At the current rate, the number of people who die from illegal drug overdoses in Tazewell County this year will top the previous four-year average and could top out twice as high as last year's total.

Heroin was the county's single deadliest drug of choice from 2008-11. Ironically, every one of the four drug deaths so far this year came from overdoses of methadone, the prescription drug designed to treat heroin addiction.

A fifth methadone death appears likely to be confirmed when the case of Grace Riviere, 19, goes before a county coroner's inquest jury on May 1.

Riviere, of 413 Sherwood Drive in Pekin, died Feb. 20 in a residence in the 1600 block of North Fourth Street. Autopsy results remain inconclusive pending toxicology test results that will be revealed at the inquest, said Tazewell County Coroner Carl Powell.

Police, however, have learned that she had twice the lethal level of methadone in her body, said Pekin Police Public Information Officer Don Jolly.

Her boyfriend said that after she had done drugs at the Fourth Street residence the night before, "She never woke up," Jolly said. Her boyfriend didn't call for help until it was too late, Jolly said. Police continue to investigate the death, which has yet produced no criminal charges.

Riviere's death is one of six throughout Tazewell in recent weeks whose cause remains undetermined pending inquests but which could include drugs as factors, Powell said. They also include the deaths in Pekin of Bryan Morse, 25, and Casey Fleeharty, 26, last week.

The number of overdose deaths in Tazewell rose from 11 in 2010 to 19 last year. The county has seen an annual drug death average of 15.5 over the past four years, according to coroner's office statistics.

Heroin and morphine, grouped together in the analysis, accounted for about 20 percent of the total 62 overdose deaths from 2008-11. Among all fatal drugs and combinations of them in that period, heroin-morphine at 12 was the only one to produce deaths in double digits.

Methadone and other prescription drugs as a group, however, killed more people than cocaine did over the period. This year, methadone has raced from the gate in a deadly gallup.

It's too soon to say why that's happened and whether it will continue, Powell said. Tazewell may be no different than elsewhere in the emergence of methadone from medical clinics, where it's distributed by prescription as a treatment to wean away heroin addiction, onto the streets.

Addicts often sell their doses for cash to buy more heroin, said Powell, a former Pekin police lieutenant.

Methadone "is a strange animal," he said. "Doctors use it as a pain killer, but it's also given in clinics to combat heroin addiction. If someone is not used to using it, they might take more than their body can handle" and die as a result, he said.